Scientists at the University of South Florida and the University of Miami found that people with mild cognitive impairment (MCI), or memory loss, who had high levels of caffeine in their blood did not go on to development dementia.
The findings indicate that caffeine, the source of which was mainly coffee, offers some protection against the onset of Alzheimer's disease, the researchers said.
In the study, the team monitored 124 people aged between 65 and 88, testing their blood caffeine levels and their cognitive ability for two to four years. They found caffeine levels among those who developed dementia were 51 per cent lower than those who did not.
"Coffee would appear to be the major or perhaps only source of caffeine for such stable MCI patients. This case- control study provides the first direct evidence that caffeine intake is associated with a reduced risk of dementia or delayed onset, particularly for those who already have MCI," the researchers wrote.
The researchers had earlier established a link between caffeine and the delayed development of Alzheimer's disease through studies of mice.
The new study showed that no one with MCI who developed Alzheimer's disease had blood caffeine levels of 1200 ng/ml -- the equivalent of several cups of a coffee.
"This study provides an intriguing association between plasma caffeine levels in MCI patients and their ensuing progression (or not) to dementia," the study added.
"High plasma caffeine levels in MCI patients at the beginning of a 2